1. Field of the Invention
The present invention relates to a hydrophilic composition useful for forming a hydrophilic film having excellent soiling resistance, fogging resistance and rapid driability in wet with water or the like and having better abrasion resistance, on the surface of various substrates, and to a hydrophilic member having a soiling-resistant and fogging-resistant surface provided with a hydrophilic film formed of the hydorpohilic composition and having excellent soiling resistance.
2. Description of the Related Art
Various techniques have been proposed for preventing adhesion of oily soil to the surface of members. In particular, optical members such as antireflection films, optical filters, optical lenses, eyeglass lenses and mirrors may be soiled with fingerprints, sebum, sweat, cosmetics and the like when used by persons, whereby their functions may lower and it is troublesome to remove the soil, and therefore it is desired to apply effective anti-soiling treatment to them.
With the recent popularization of mobiles, displays have become much used in the outdoors; but when they are used in the environment in which external light is incident thereon, they cause some problems in that the incident light may make mirror reflection on them and the reflected light may mix with the display light to make the display image difficult to see. Accordingly, an antireflective optical member is often disposed on the surface of displays.
As the antireflective optical member of the type, for example, known are a laminate of a high-refractivity layer and a low-refractivity layer; a structure having a low-refractivity layer of an inorganic or organic fluoride compound singly formed on the surface of a transparent substrate; and a structure constructed by forming a coating layer containing transparent fine particles on the surface of a transparent plastic film substrate, in which the roughened surface may thereby make irregular reflection of external light on it. Like that of the above-mentioned optical members, the surface of the antireflective optical members may be readily soiled with fingerprints, sebum and the like when used by persons, and therefore they have some problems in that the only soiled part may make high reflection thereon and the soil becomes more remarkable and, in addition, the surface of the antireflection film generally has fine projections and recesses and therefore soil removal from it is difficult.
Various techniques have been proposed for forming, on the surface of solid members, an anti-soiling function having a capability of making the surface difficult to soil and a capability of facilitating removal of the soil adhering thereto. In particular, as a combination of an antireflective member and an anti-soiling member, for example, proposed are a soiling-resistant and abrasion-resistant material having an antireflection film of essentially silicon dioxide and processed with an organosilicon substituent-having compound (e.g., see JP-A 64-86101); and a soiling-resistant and abrasion-resistant CRT filter in which the substrate surface is coated with a silanol-terminated organopolysiloxane (e.g., see JP-A 4-338901). Also proposed are an antireflection film containing a silane compound such as typically a polyfluoroalkyl group-having silane compound (e.g., see JP-B 6-29332); and a combination of a thin optical film of essentially silicon dioxide and a copolymer of a perfluoroalkyl acrylate and an alkoxysilane group-having monomer (e.g., see JP-A 7-16940).
However, the soiling-resistant layer formed according to conventional methods is insufficient in point of its soiling resistance and, in particular, soil with fingerprints, sebum, cosmetics and the like is difficult to wipe off, and the surface treatment with a material having low surface energy such as fluorine, silicon or the like is problematic in that the anti-soiling capability of the treated surface may lower with time, and therefore, it is desired to develop an anti-soiling member having excellent soiling resistance and durability.
A resin film or an inorganic material of glass, metal or the like that is generally used as the surface of optical members is generally hydrophobic or weakly hydrophilic on its surface. When the surface of a substrate formed of such a resin film or an inorganic material is hydrophilicated, then water droplets adhering thereto may uniformly spread on the substrate surface to form a uniform water film thereon, and accordingly, this may be effective for preventing glass, lenses and mirrors from fogging, and may be helpful for preventing devitrification and for securing view even in rain. Further, hydrophobic pollutants, for example, combustion products such as carbon black in city dust and exhaust gas by vehicles, and also oils and fats and ingredients released from sealants may hardly adhere to it, and even if they have adhered thereto, they may be readily removed by rain or washed away with water; and therefore the resin film and the inorganic material are useful in various applications.
Surface treatment for hydrophilication heretofore proposed, for example, etching treatment or plasma treatment enable high-level surface hydrophilication, but its effect is temporary and the hydrophilicated condition could not be kept as such for a long period of time. Also proposed is a surface-hydrophilicating coating film formed of a hydrophilic graft polymer, a type of a hydrophilic resin (e.g., see Article of Daily Newspaper Chemical Industry, Jan. 30, 1995); however, though this coating film may have hydrophilicity in some degree, its affinity to substrates is not sufficient, and a coating film having higher durability is desired.
As a film having excellent surface hydrophilicity, heretofore known is a film comprising titanium oxide. For example, disclosed is a technique of forming a photocatalyst-containing layer on the surface of a substrate, and then highly hydrophilicating the surface in accordance with the optical excitation of the photocatalyst; and it is reported that, when this technique is applied to various composite materials such as glass, lenses, mirrors, exterior materials and water supply members, then it may give excellent soiling resistance to those composite materials (e.g., see WO96/29375). However, since the hydrophilic film comprising titanium oxide does not have a sufficient film strength and since it could not exhibit its hydrophilicating effect when not subjected to optical excitation, it has a problem in that its applicable sites are limited. Accordingly, an anti-soiling member having durability and having good abrasion resistance is desired.
To solve the above-mentioned problems, the characteristics of a sol-gel organic-inorganic hybrid film have been specifically noted, and it has been found that a hydrophilic surface having a crosslinked structure formed through hydrolysis and polycondensation of a hydrophilic polymer and an alkoxide has excellent fogging resistance and soiling resistance and has good abrasion resistance (see JP-A 2002-361800). The hydrophilic surface layer having such a crosslinked structure may be readily formed by combining a specific hydrophilic polymer having a reactive group at its terminal and a crosslinking agent.